1. Field of the Invention
The present invention relates to a radar module for use in an FM millimeter-wave radar alarm system for use on motor vehicles, and an MMIC (Monolithic Microwave Integrated Circuit) package for use in such a radar module.
2. Description of the Prior Art
One known motor vehicle radar alarm system has an electronically scanning planar array antenna as disclosed in U.S. Pat. No. 5,008,678. The disclosed electronically scanning planar array antenna comprises a plurality of transmitting and receiving planar antenna elements, a pair of passive phased arrays such as planar microstrip Butler matrixes, and a pair of electronic switches which are combined to transmit and receive a scanning beam.
The conventional electronically scanning planar array antenna is disadvantageous in that the passive phased arrays thereof cannot scan a relatively large angular range with the scanning beam. Another problem is that the planar array antenna requires both a transmitting array of antenna elements dedicated for transmitting a radar signal and a receiving array of antenna elements dedicated for receiving an echo signal, posing limitations which make it difficult to reduce the size of the planar antenna array and, especially, to install the planar array antenna on a motor vehicle.
Japanese laid-open patent publication No. 4-129402 discloses an MMIC package which may be used in the above electronically scanning planar antenna array. The disclosed MMIC package includes a metal substrate supporting on one surface thereof a high-frequency integrated circuit (MMIC) and a multilayer substrate with a conductive pattern disposed thereon. The MMIC package also includes a low-frequency drive circuit substrate which confronts and is spaced from the high-frequency integrated circuit, the low-frequency drive circuit substrate serving as a lid of the MMIC package. The high-frequency integrated circuit and the low-frequency drive circuit substrate are electrically connected to each other by the conductive pattern on the multilayer substrate and conductive paths on a frame by which the low-frequency drive circuit substrate is mounted on the multilayer substrate.
The high-frequency integrated circuit is enclosed and sealed by the lid, i.e., the low-frequency drive circuit substrate, and the frame. Since they are enclosed and sealed by the low-frequency drive circuit substrate and the frame, the circuits are installed at a high density in the MMIC package even if the MMIC package has a relatively small volume.
However, since the high-frequency integrated circuit on the metal substrate and the low-frequency drive circuit substrate as the lid are electrically connected through the conductive paths on the frame, it is difficult to position the metal substrate and the low-frequency drive circuit substrate accurately with respect to each other for providing electric connections between conductors on those substrates. Therefore, the electric connections that are established between conductors on those substrates are liable to suffer reliability problems.
Particularly if the MMIC package is small in size, junctions for the conductors are also small in dimensions and hence cannot easily be connected physically. As a consequence, the reliability of electric connections between the high-frequency integrated circuit and the low-frequency drive circuit substrate tends to be low.
The MMIC package including the high-frequency integrated circuit and the low-frequency drive circuit substrate cannot be checked for its overall functions until lead terminals are attached to the package assembly and the package assembly is then encased by a molding thereby to complete the MMIC package. Therefore, in the event of a conduction failure detected between the high-frequency integrated circuit and the low-frequency drive circuit substrate by the function check, the lead terminals and the MMIC package become useless, and the time, labor, and cost which have been required to produce the MMIC package are wasted. For the above reasons, the conventional MMIC packages are relatively expensive to manufacture.
Recent high-frequency integrated circuits for use in radar alarm systems on motor vehicles for collision prevention and driving guidance operate in a microwave frequency range from 1 GHz to 3000 GHz. There has been a demand for hybrid ICs comprising high- and low-frequency integrated circuits, which operate in respective GHz and MHz frequency ranges, in order to reduce a packaging space and increase a module density for the purpose of installing a plurality of high-frequency integrated circuits (MMICs) on one substrate.
In such hybrid ICs, it is necessary to position the high- and low-frequency integrated circuits in an appropriate layout to avoid unwanted interference between those high- and low-frequency integrated circuits.